Transistorized flasher circuit

ABSTRACT

A transistorized flasher circuit for vehicle signal lamps comprising a free running multivibrator, incorporating a capacitor and a programmable unijunction transistor, for cyclically and intermittently driving an output transistor into a conductive state as the capacitor is alternately charged and discharged. A relay is provided and includes a coil connected in series with the output circuit of the output transistor and a set of normally open contacts which are connected in series with a lamp load and a start switch and which are closed in response to the energization of the coil. A charging circuit including the capacitor and a diode connected in series therewith is connected in parallel with the set of relay contacts for charging the capacitor along a first path when the set of relays contacts open. A discharging circuit is provided for discharging the capacitor along a second path, which does not include the diode, when the relay contacts close.

United States Patent 1191 Alten Apr. 17, 1973 TRANSISTORIZED FLASHER CIRCUIT [75] Inventor: Ralph W. Alten, East Detroit, Mich.

FOREIGN PATENTS OR APPLICATIONS 1,217,824 /1966 Germany ..340/81 sslgnee 23 {:S Inc Fort Primary Examiner-John W. Caldwell Assistant Examiner-Kenneth N. Leimer [22] Filed: July 28, 1970 Attorneyl.earman & McCulloch [21] Appl. No.: 58,919 1. ABSTRACT A transistorized flasher circuit for vehicle signal lamps [52] 307/252 315/200 comprising a free running multivibrator, incorporating I I14 331/1 1 340/81 R a capacitor and a programmable unijunction [51] Int. Cl. ..B60q U38, HOSb 39/09 transistor for cyclically and intermittently driving an of Search 81, 82, 83, t t t i t i a d ti t as th a aci- 340/3311307/132 51315/209 210, 217; tor is alternately charged and discharged. A relay is 317/ 141 5 provided and includes a coil connected in series with the output circuit of the output transistor and a set of References Cited normally open contacts which are connected in series with a lamp load and a start switch and which are UNITED STATES PATENTS closed in response to the energization of the coil. A 2,891,195 6/1959 Smyth ..34o/331x Charging circuit including the capacitor and a diode 3,002,127 9/1961 Grontkowski 340/81 x connected in series therewith is connected in parallel 3,113,242 12/1963 Leeder ..340/331 X with the set of relay contacts for charging the capaci- 3,263,123 7/1966 Leeder ....340/81 UX tor along a first path when the set of relays contacts 3,281,611 10/1966 Leeder ..340/81 X open. A discharging circuit is provided for discharging 3,413,519 11/1968 Leeder ..340/331 X the capacitor along a second path, which does not in- 3,447,03I 5/l969 .lenks X clude the diode when thg relay contacts close 3,452,248 6/1969 Leeder ..340/8l UX 3,493,313 7 2/279 Seidler ..340/33l X 2 Claims, 1 Drawing Figure 3,445,810 5/l969 Donoh0o ..340/73 X 3,576,444 4/1971 Roberts, "1340/81 E 3,601,795 8/1971 Shimizu et al ..340/l76 X 9 f 13 ID llile l I 40 i 12 I5 46 48 14 I y ==L i L 42 17 20 g PATENTEDAPRITIW I 'v ':a;728',v13

'INVENTOR RALPH W. ALTEN ATTORNEYS TRANSISTORIZED FLASHER CIRCUIT FIELD OF THE INVENTION This invention relates to automotive signal lamp circuits and more particularly to a transistorized signal lamp flasher circuit employing a relay and being operable in a manner which is substantially independent of the relay characteristics.

DESCRIPTION OF THE PRIOR ART Prior art flasher circuits incorporating relays have been proposed heretofore, but their operation in most instances has been dependent upon the load and'the voltage values at which the relay coil is operable to close and open the relay contacts. In such circuits, should the output of the operating voltage source fall below the pull in voltage of the relay, the circuit will not function properly. Moreover, the frequency at which the signal lamps flash is dependent upon the strength of the voltage source and, as the output of the source decreases, the frequency also decreases.

The prior art flasher circuits also are rather large and unwieldy and incorporate a substantial number of parts which prevents their being assembled compactly with the relays controlled thereby.

An object of this invention is to provide a flasher circuit, incorporating a relay, for intermittently energizing a lamp load and which operates at a frequency which is not load sensitive and is substantially independent of the relay operating characteristics.

Another object of the invention is to provide an intermittently energized flasher circuit composed of substantially fewer parts than previously have been required.

Other objects and advantages of the invention will be pointed out specifically or will become apparent from the following description.

A transistorized flasher circuit constructed according to the invention and adapted for use in conjunction with vehicle signal lamps comprises a relay having an operating coil connected in the output circuit of a transistor and a set of relay contacts connected with a series circuit including a manually operable switch and a lamp load. A free-running multivibrator, including a programmable unijunction transistor, is provided for cyclically and intermittently triggering the transistor between its conductive and non-conductive states and includes a resistance-capacitance charging circuit serially connected with a diode across the relay contacts for periodically rendering the programmable unijunction transistor conductive. The charging circuit automatically is isolated from its charging source and the load when the relay contacts close.

The invention more readily may be understood by reference to the accompanying drawing wherein the single FIGURE is a schematic diagram of a circuit embodying the invention.

A transistorized flasher circuit constructed according to the preferred embodiment of the invention is adapted to be connected to a source of direct current which may be a conventional vehicle storage battery having its negative terminal connected to a common ground 12 and its positive terminal connected to a junction 13. A relay operating coil 14 is connected to contacts 14a which also are connected to the junction 13. The contacts 14a are closed when the relay operating coil 14 is energized. An NPN junction transistor 16 includes a collector electrode 17 connected to the operating coil 14 and an emitter electrode 18 at ground potential. A free-wheeling diode 15 of known construction is connected in parallel with the relay coil 14 to suppress the inductive voltage transient which otherwise would occur across the coil when the transistor 16 is rendered non-conductive.

The set of relay contacts 144 is connected in series circuit with the manually movable armature 20 of a turn signal selector switch S having neutral, left, and right output contacts 22, 23, and 24, respectively, which are selectively engageable by the armature 20. The contacts 23 and 24 are connected with left-hand and right-hand signal lamps 26 and 28, respectively, which are at ground potential.

To render the transistor 16 conductive and non-conductive, a free-running multivibrator oscillator circuit, generally shown in chain lines at O, is provided and includes a four-layer programmable unijunction transistor 30 having an anode electrode 31, a gate anode electrode 32, and a cathode electrode 33. A programmable unijunction transistorsuch as that made by General Electric Company and designated Model Dl3Tl is suitable.

The gate electrode 32 is connected to the junction of the resistors 35 and 36 which are connected in series across the source 10 between the junction 13 and ground 12. The resistors 35 and 36 function as a voltage divider and control the voltage at which the anode to gate junction of the programmable unijunction transistor 30 becomes forward biased. The cathode 33 of the unijunction transistor 30 is connected to the base electrode 39 of the transistor 16 and also is connected to a load resistor 38 which is connected to ground potential. The potential drop across the resistor 38 controls the conduction of transistor 16 which functions as an electronic switch.

The oscillator circuit 0 includes a capacitor 42 serially connected to a resistor 40 which is connected to the junction 13. The anode 45 of a diode 44 is connected to the capacitor 42 and the cathode of the diode 44 is connected to the movable armature 20 of the turn signal selector switch. The resistor 40, the capacitor 42, and the diode 44 thus provide a capacitor charging circuit connected in parallel with the relay contacts 14a for charging the capacitor 42 only when the relay contacts 14a are open. A resistor 46 is connected in parallel with the resistor 40 and the capacitor and provides a discharge path for the capacitor 42. The emitter 31 of the programmable unijunction transistor 30 is connected to the junction 48 between the resistor 40 and the capacitor 42.

In an operating embodiment of the invention, the following circuit constants were found suitable for obtaining a flash rate of per minute:

Source l0 12 volts Relay coil 14 66 ohms Resistor 35 l Kohm Resistor 36 3.3 Kohm Resistor 38 22 Kohm Resistor 40 220 Kohm Resistor 46 680 Kohm Transistor l6 2N34l Transistor 30 Dl3Tl Capacitor 42 1.0 Microfd.

THE OPERATION When the switch 20 is in the neutral position shown in the drawing, the relay coil 14 will not be energized and the contacts 14a will be opened. When the operator moves the turn signal switch armature 20 from the neutral position to engage the contact 24, for example, for the purpose of operating the lamp 28, a circuit will be completed from the source through the resistor 40, the capacitor 42, the diode 44, the armature 20, and the lamp 28 to initiate charging of the capacitor 42. Because of the relatively high resistance of the resistor 40, the charging current is insufficient to illuminate the lamp 28. When the capacitor 42 has been charged so that the voltage at the junction 48 is sufficient to forward bias the anode to gate junction of the programmable unijunction transistor 30, the regeneration inherent in the four-layer programmable unijunction transistor causes the transistor 30 to become conductive and cause a current flow through the resistor 38 to ground. The voltage drop across the resistor 38 will be such as to forward bias the emitter to base junction of the transistor 16 so as to render the transistor 16 conductive. Current thus will flow from the source 10 through the relay coil 14 and the collector 17 and the emitter 18 of the transistor 16. When the relay coil 14 is energized, the contacts 14a will close to provide a circuit for lamp illuminating current to flow from the source 10, through the contacts 14a, the switch 20, and the lamp load 28. a

When the contacts 14a close it is important to note that the charging circuit including resistor 40, capacitor, 42, and diode 44 will be automatically isolated from the source 10 in that the potential of the switch armature 20 will approach the potential of junction 13. The capacitor 42 then discharges through the resistor 40 and the resistor 46 so as to reduce the voltage of the junction 48 by an amount sufficient to reverse bias the anode to gate junction of the programmable unijunction transistor 30 and thus render it non-conductive. The potential at the switch 20 reverse biases the diode 44 and permits the capacitor 42 to discharge through the resistor 46. The capacitor 42 is also automatically isolated from the load 28 and the discharge rate of capacitor 42 is, therefore, not load sensitive. Thus the length of time that the transistors 30 and 16 remain conductive is independent of the load and the length of time that the lamp 28 is lighted and remains substantially constant. When the current flow through the resistor 38 ceases, the transistor 16 is rendered non-conductive, thus deenergizing the winding 14 whereby the contacts 140 will open to darken the lamp 28. The capacitor 42 thereupon again charges through the diode 44 and the cycle is repeated. The circuit is independent of load and is unaffected by the relay characteristics since the wave form of the voltage in the output circuit of the transistor 16 is substantially square.

When the capacitor 42 is being charged, the diode 44 is forward biased and the charging time is determined primarily by the resistance of the resistor 40. However, when the capacitor 42 is discharging, the diode 44 is reverse-biased because the emitter end 45 of the diode 44 is then negative. As long as the capacitor 42 is charged, the discharge current must flow through the resistor 46. Thus, the discharging time is determined by the resistance of both of the resistors 40 and the resistors 46. Consequently, the on and off" times of the unijunction transistor 30 and the lamps 26 and 28 are controlled by the values of the resistors 40 and 46. If the resistor 46 is approximately twice the resistance of resistor 40, the on and off" times are approximately equal.

The disclosure is intended to be illustrative rather than definitive of the invention. The invention is defined in the claims.

I claim:

1. A flasher circuit comprising:

a source of unidirectional electric potential;

a junction transistor having emitter, collector and base electrodes;

a relay having an operating coil and normally disengaged contacts which are movable into engagement in response to energization of said coil, said operating coil being serially connected with said source and the emitter and collector electrodes of said junction transistor, said contacts being connected to said source and a series circuit comprising a manually operable switch and a lamp load;

a diode connected to the junction of said contacts and said series circuit; and

circuit means connected to said source and including:

a capacitor charging circuit connected to said relay contacts and including a first resistor and a capacitor connected in series with said diode to provide a charging path for capacitor charging current when said contacts are disengaged, discharging circuit including a second resistor connected in parallel with said first resistorand said capacitor to provide a discharging path for capacitor discharging current when said contacts are engaged, programmable unijunction transistor including anode, gate, and cathode electrodes, said anode electrode being connected to the junction of I said first resistor and said capacitor,

a voltage divider connected to said source, and

a third resistor connected to said source,

said gate electrode being connected to said voltage divider,

said cathode electrode being connected to said third resistor and to the base electrode of said junction transistor.

2. A flasher circuit, adapted to be connected to a source of unidirectional electric potential, for intermittently energizing a signal lamp, comprising:

a relay including an electrically energizable operating coil, and a pair of contacts adapted to be connected to said source and movable between disengaged and engaged positions in response to energization and deenergization of said operating coil;

a lamp load;

switch means connected in circuit with said pair of contacts and said lamp load and being movable between a closed position and an open position for respectively connecting and disconnecting said lamp load to and from said source through said pair of contacts in the engaged position;

a transistor having base, emitter and collector electrodes, said emitter and collector electrodes being connected in series with said operating coil for establishing current flow from said source to said circuit means connected operating coil when said transistor is conductive so that said pair of contacts is moved to said engaged positions to energize the lamp load; and

in circuit with said transistor and said switch means and operable upon application of said electric potential thereto, when said switch means moves to said closed position, to cyclically and intermittently trigger said transistor between conductive and non-conductive states and cyclically establish current flow from said source through said emitter and collector electrodes and said operating coil so that said pair of contacts move between said disengaged and said engaged positions and energize the lamp load;

said circuit means comprising a series charging circuit, connected in parallel circuit with said pair of contacts, including a first resistor, a chargeable and dischargeable capacitor, and a diode connected to said switch means permitting the flow of current in a first direction to said switch means and said load when said contacts are in said disengaged positions and for blocking a reverse flow of current isolating said first resistor and capacitor from said lamp load when said contacts are in said engaged positions;

a discharging circuit including a second resistor connected in parallel with said first resistor and said capacitor providing a discharge path for said capacitor when said contacts are in said engaged positions; and

a programmable unijunction transistor having anode, gate, and cathode electrodes, said anode electrode being connected to the junction of said capacitor and said first resistor, said gate electrode being adapted to be connected in circuit with said source, said cathode electrode being connected to said base electrode. 

1. A flasher circuit comprising: a source of unidirectional electric potential; a junction transistor having emitter, collector and base electrodes; a relay having an operating coil and normally disengaged contacts which are movable into engagement in response to energization of said coil, said operating coil being serially connected with said source and the emitter and collector electrodes of said junction transistor, said contacts being connected to said source and a series circuit comprising a manually operable switch and a lamp load; a diode connected to the junction of said contacts and said series circuit; and circuit means connected to said source and including: a capacitor charging circuit connected to said relay contacts and including a first resistor and a capacitor connected in series with said diode to provide a charging path for capacitor charging current when said contacts are disengaged, a discharging circuit including a second resistor connected in parallel with said first resistor and said capacitor to provide a discharging path for capacitor discharging current when said contacts are engaged, a programmable unijunction transistor including anode, gate, and cathode electrodes, said anode electrode being connected to the junction of said first resistor and said capacitor, a voltage divider connected to said source, and a third resistor connected to said source, said gate electrode being connected to said voltage divider, said cathode electrode being connected to said third resistor and to the base electrode of said junction transistor.
 2. A flasher circuit, adapted to be connected to a source of unidirectional electric potential, for intermittently energizing a signal lamp, comprising: a relay including an electrically energizable operating coil, and a pair of contacts adapted to be connected to said source and movable between disengaged and engaged positions in response to energization and deenergization of said operating coil; a lamp load; switch means connected in circuit with said pair of contacts and said lamp load and being movable between a closed position and an open position for respectively connecting and disconnecting said lamp load to and from said source through said pair of contacts in the engaged position; a transistor having base, emitter and collector electrodes, said emitter and collector electrodes being connected in series with said operating coil for establishing current flow from said source to said operating coil when said transistor is conductive so that said pair of contacts is moved to said engaged positions to energize the lamp load; and circuit means connected in circuit with said transistor and said switch means and operable upon application of said electric potential thereto, when said switch means moves to said closed position, to cyclically and intermittently trigger said transistor between conductive and non-conductive states and cyclically establish current flow from said source through said emitter and collector electrodes and said operating coil so that said pair of contacts move between said disengaged and said engaged positions and energize the lamp load; said circuit means comprising a series charging circuit, connected in parallel circuit with said pair of contacts, including a first resistor, a chargeable and dischargeable capacitor, and a diode connected to said switch means permitting the flow of current in a first direction to said switch means and said load when said contacts are in said disengaged positions and for blocking a reverse flow of current isolating said first resistor and capacitor from said lamp load when said contacts are in said engaged positions; a discharging circuit including a second resistor connected in parallel with said first resistor and said capacitor providing a discharge path for said capacitor when said contacts are in said engaged positions; and a programmable unijunction transistor having anode, gate, and cathode electrodes, said anode electrode being connected to the junction of said capacitor and said first resistor, said gate electrode being adapted to be connected in circuit with said source, said cathode electrode being connected to said base electrode. 